SYDNEY (AP) -- Five people escaped from a Sydney cafe where a gunman took an unknown number of hostages during Monday morning rush hour. Two people inside the cafe earlier held up a flag with an Islamic declaration of faith that has often been used by extremists, raising fears that a terrorist incident was playing out in the heart of Australia's biggest city.

The first three people ran out of the Lindt Chocolat Cafe in downtown Sydney six hours into the hostage crisis, and two women sprinted from a fire exit into the arms of waiting police shortly afterward. Both women were wearing aprons with the Lindt chocolate logo, indicating they were cafe employees.

As the siege entered its 12th hour Monday night, basic questions remained unanswered. Police refused to say how many hostages were inside the cafe, what they believed the gunman's motives might be, whether he had made any demands or whether the hostages who fled the cafe escaped or were released.

"I would like to give you as much as I can but right now that is as much as I can," New South Wales state police Commissioner Andrew Scipione said. "First and foremost, we have to make sure we do nothing that could in any way jeopardize those still in the building."

The AP report notes:

Television video shot through the cafe's windows showed several people with their arms in the air and hands pressed against the glass, and two people holding up a black flag with the Shahada, or Islamic declaration of faith, written on it.

The Shahada translates as "There is no god but God and Muhammad is his messenger." It is considered the first of Islam's five pillars of faith, and is similar to the Lord's Prayer in Christianity. It is pervasive throughout Islamic culture, including the green flag of Saudi Arabia. Jihadis have used the Shahada in their own black flag.

Sydney (CNN) -- A gunman holding hostages in a Sydney cafe is said to be demanding an ISIS flag and a phone call with Australian Prime Minister Tony Abbott.

The reported demands emerged after five hostages managed to flee the building, leaving an unconfirmed number of people still trapped inside during a standoff that has lasted more than 12 hours so far.

Hours into the siege, the gunman's requests were made through hostages who contacted several media organizations, CNN affiliate Sky News Australia reported.

Police said they were aware of the reports but declined to confirm what demands had been made.

Amid the crisis, hundreds of police officers, some of them armed with sniper rifles, shut down a usually bustling area in Australia's most populous city.

More from CNN:

Footage showed (hostages) holding up a black flag with Arabic writing on it that reads: "There is no God but God and Mohammed is the prophet of God." That flag was different from the one used by the terrorist group ISIS.

Australians came together in a social expression of solidarity with Australian Muslims, using the #IllRideWithYou hashtag to offer to accompany people wearing Muslim dress who were concerned about a backlash amid the Sydney cafe siege.

Armed police shut down central Sydney Monday after a suspected gunman took several people hostage in a cafe and placed an Islamic flag in the window.

The social gesture started with this tweet, with this person offering to support and walk with a woman wearing a hijab.

Even as facts on the hostage situation remain sketchy, AP provides this insight:

The Islamic State group, which now holds a third of Syria and Iraq, has threatened Australia in the past. In September, Islamic State group spokesman Abu Mohammed al-Adnani issued an audio message urging so-called "lone wolf" attacks abroad, specifically mentioning Australia. Al-Adnani told Muslims to kill all "disbelievers," whether they be civilians or soldiers.

One terrorism expert said the situation appeared to be that of a "lone wolf" making his own demands, rather than an attack orchestrated by a foreign jihadist group.

"There haven't been statements from overseas linking this to extremist groups outside the country - that is quite positive," said Charles Knight, lecturer in the Department of Policing, Intelligence and Counter Terrorism at Australia's Macquarie University. "The individual or individuals involved didn't kill early, which is part of the pattern of some recent international attacks. ... It seems to be shifting more into the model of a traditional hostage situation, rather than the sort of brutal attacks we've seen overseas."